The present invention relates to railway tank cars, and particularly such tank cars adapted for interconnection to accommodate loading and unloading of a train of interconnected cars without movement thereof, structure being provided for singly and sequentially loading the tank cars with fluid lading and singly and sequentially unloading the tank cars of fluid lading, and loading and unloading systems for a train of such tank cars.
The concept of providing fluid communication among a series of interconnected railway tank cars is disclosed in the prior art, but previous systems have failed to provide a valve mechanism and control system therefor useful during loading and unloading of fluid ladings that would safely handle certain types of fluid ladings such as compressed liquified gases, and particularly liquified petroleum gases. For example, prior U.S. Pat. No. 3,897,807 granted Aug. 5, 1975 to D. Hurst and myself discloses a unit train of tank cars with the tanks thereof connected in series, and also discloses in FIGS. 16 to 19A thereof a train of tank cars wherein the individual tanks are connected by input-output conduits 320 and bypass pipe sections 330 with control valves 335 therein, whereby the individual tanks in the unit train can be filled either serially, i.e., one after the other with fluid ladings flowing sequentially through each of the tanks, or alternatively, the tanks can be loaded in parallel thus permitting substantially simultaneous loading of the tanks. When handling certain fluid ladings, such as liquified petroleum gases, such loading and unloading procedures are not practicable and present safety hazards.
U.S. Pat. No. 1,542,116 granted June 16, 1925 to R. Welcker discloses railway tank cars for interconnection in a manifolded arrangement to accommodate continuous emptying of the interconnected tanks from a single location, without moving or disconnecting the cars. However, the arrangement of the Welcker patent does not provide for continuous loading of the interconnected tanks from a single location in a sequential manner, and the inter-tank lading connections are along the longitudinal axes of the tanks which is found to be a disadvantageous arrangement.
U.S. Pat. No. 3,675,670 granted July 11, 1972 to O. Ogawa shows railway tank cars for interconnection in a manifolded arrangement to accommodate continuous loading and unloading of the interconnected tanks from a single location. However, the tank cars of the Ogawa patent are not suitable for handling of liquified petroleum gases, and the like, and would present hazards in the loading operation and the unloading operation and also during transportation of the loaded tank cars.
U.S. Pat. No. 3,722,556 granted Mar. 27, 1973 to W. Jeffers and J. M. Jeffers discloses a manifolded tank arrangement which accommodates both loading and unloading of a string of interconnected tank cars from a single location, but provides the inter-tank lading connections at the bottom of the tanks, and provides exposed and unprotected lading flow control valves whereby to present a substantial safety hazard during transport of the tank cars.
While the tank car, the loading system and the unloading system of the present invention can be utilized with various liquid ladings or commodities, the tank car and the loading and unloading systems are primarily intended for use in the transportation of liquified compressed gases, and specifically liquified petroleum gases, wherein safety is of paramount importance. The present invention provides a system wherein in the normal loading operation of a string or train of tank cars, only a single tank car will be in liquid communication with the lading conduit or loading line at any one time; likewise, in the normal unloading operation of a string of tank cars, only a single tank car will be in liquid communication with the lading conduit or unloading line at any one time. More specifically during the loading operation, the gas or vapors that remain in the as yet unloaded tank cars are pushed through the tank cars serially while the liquid lading is loaded into the tank cars singly and in sequence, and actually in parallel one with the other but singly. In the unloading of a train of the tank cars, the compressed gas used to unload the tank cars is pushed through the tank cars in series so as to provide for maximum ventilation thereof, while the liquid lading is removed from the tank cars singly and sequentially and therefore in parallel but singly. This arrangement provides safety in the case of rupture of one of the conduits during the loading or unloading since but a single car is exposed at any one time to the dangerous liquid lading. There also is a minimum pressure drop in the system during the loading and unloading operations since only a single tank car is loaded or unloaded at any one time. All this is accomplished while providing a system that is compatible with the present transportation systems for such liquified compressed gases.
The prior art on the other hand provides systems wherein there is a significant pressure drop along the loading and unloading conduits since the tank cars are essentially connected in series during both the loading and unloading operations. Rupture in the loading line or the unloading line of the prior art structures provides a more serious safety hazard when all the tank cars are serially connected since there is no reservoir to receive lading in the event of rupture of one of the conduits.
The arrangement of the present invention provides a safer system in that a minimal number of controls are required for the system, and a minimum number of openings are required into each tank car. In the prior art on the other hand, there were in general more openings required and more controls required, whereby more protective structure must be provided therefor.
As will appear more fully hereinafter, the electrical-pneumatic control system for the present invention includes a pneumatic accumulator which provides a fail-safe reservoir for operating the various control valves to close off the tank cars and the lading conduits in the event of the breaking of any of the pneumatic lines. The accumulator is incorporated in the system so as automatically to close the valves in the lading conduit upon completion of the loading of the tank cars and to close the valves for the pipes leading into the tank cars upon completion of the unloading of the tank cars.
An additional safety feature resides in the provision of a system wherein the failure of any electronic component in a single tank car will not disrupt the loading procedure but enables continued loading of the next and subsequent tank cars in a train of the tank cars. More specifically, upon the failure of an electronic component of the second car in a string of tank cars so that the second tank car is not in readiness for loading or in the event of failure of any of the valving in the second tank car which would prevent loading thereof, the lading conduit across the second tank car is still open and loading can proceed with the third tank car or any subsequent tank car which is in condition for loading. Each of the control valves on the tank cars includes a position indicator so that the operator can immediately detect that one of the tank cars is not operating properly and can take steps thereafter to repair or remedy the malfunction on the second tank car, for example, while loading proceeds with subsequent tank cars. As soon as the second tank car is repaired and placed in operative condition again, loading of that tank car can proceed without interruption of the loading operation.